An accurate but lengthy procedure to measure moisture content, whereby a sample piece of the respective wood is weighed. The sample piece is then dried for several hours at around 100°C in a kiln that is heated with electricity, and is then weighed again (dry weight = darr weight). In calculating the moisture content of wood in percent, the water content of the sample pieces is compared with their darr weight. [ Moisture content in % = wet weight in g - darr weight in g ÷ darr weight in g x 100 ]

Since wood constantly endeavours to adjust its moisture to the surrounding climate (temperature and relative huminity), it either absorbs moisture from the air or it releases moisture. This adjustment is linked to dimensional changes: The wood swells (increase in dimensions) or shrinks (decrease in dimensions). The differential expansion [“q”], which indicates by what percentage the dimensions of the wood change when the wood moisture content changes by 1%, is used as the parameter. In this context, the technical term “dimensional stability” does not describe a concrete measurable dimension, but rather 1. factors that are independent of the type of wood (structural formation, type of cut, surface treatment etc.) and 2. factors determined by the type of wood. The factors determined by the type of wood include the degree of expansion and contraction described above and the differences between the separate section planes of the wood (across the grain wood swells and shrinks more than along the grain).

Evergreen conifer with a regularly formed, conical crown. The Douglas fir grows up to 50 m high and up to almost 100 m in its region of origin (the Pacific coastal area of North America). The light earlywood of the Douglas fir has a strongly defined structure and the latewood bands have a particular narrowly streaked structure. Trees with growth ring widths of 1 mm and correspondingly narrow latewood bands produce a light heartwood called yellow fir; the coarser, darker wood is called red fir. The colour of the heartwood still darkens considerably in the light. Douglas fir wood is soft, coarse-grained, very tough and durable.